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Stihl 034 AV

SteveSr

SteveSr

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I don't have a gauge to check but lever is about .5mm (eyeball measure) below sides of carb when I place a strait edge over it.
Compare the height of the old lever against the new. If the lever is too high or the gaskets/diaphragm is in the wrong order it will leak and lead to flooding.
 
Skippydiesel

Skippydiesel

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I'd start by putting pressure on the fuel inlet. Should be able to pump it up to at least 10psi before it "pops off".
If it doesn't hold pressure drop it in a jar of water & look for where the bubbles are coming from.
If it passes the pressure test you can test the nozzle check valve by pressing a straw or tube onto it & gently suck on/blow into it... Should only flow freely towards the venturi.
As previously stated, even if the nozzle check valve has an issue, there has to be something else amiss to cause over fueling
Good morning JD - have just come in from the workshop. Done your tests:
  • Don't have anything I can control down to 10 psi so blew as hard as I could - no leak.
  • Nozzle check valve - can suck/blow air in both directions. This means I have damaged it - is there a fix?
The nozzle check valve has a brass plug on the inside - no obvious non destructive access. Could drill a small hole and use this to apply upward pressure in the hope of removing it. Replace with solder over hole.
 
SteveSr

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Don't have anything I can control down to 10 psi so blew as hard as I could - no leak.
Just because you can't test it properly doesn't mean that it isn't a problem! Definition: The longest distance between two points is... A shortcut!

Forget the main nozzle for now. You have a needle and seat leak!
 
Skippydiesel

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Okay - I guess a new
Just because you can't test it properly doesn't mean that it isn't a problem! Definition: The longest distance between two points is... A shortcut!

Forget the main nozzle for now. You have a needle and seat leak!
Okay - So a new needle valve should fix ???
 

J D

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I agree with Steve (especially the "longest distance" bit, that's gold!)
The nozzle check valve may indeed be leaking, but it can only leak excessive fuel if there is something else causing excessive fuel to be there. Put another way, it doesn't regulate the amount of fuel, only the direction the fuel flows. The amount of fuel is governed by the metering system.
At a pinch you could rig up a bike pump with a guage to see what you need to. Blowing up it isn't going to tell you anything unless it has a huge leak & you have it in a jar of water
 
Skippydiesel

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Not if it's the seat... Hasn't it got a new needle in it already?
You need to test it, or take it to someone who can
No new needle - carb kits (x 2) only came with gaskets and diaphragms.
I think my son has a bicycle pump with a gauge on it - will investigate. If not will have to take it in to town - CV 19 outbreak here, may prevent this in the short term.
Make sure your nib on the metering diaphragm is the same thickness as the old one, if is thicker this will cause major flooding.

Will check this.
 

J D

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What did you use as a cleaner when you cleaned the carb out? Some aggressive cleaners/solvents will damage the soft components like needle points, valves, diaphragms etc. That in combination with compressed air would explain a lot
 
Skippydiesel

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What did you use as a cleaner when you cleaned the carb out? Some aggressive cleaners/solvents will damage the soft components like needle points, valves, diaphragms etc. That in combination with compressed air would explain a lot
JD - carb cleaner was applied after strip and no rubber on needle valve.

Fitted new kit - so no contact with cleaner.

AND

Pressure tested system using sons bike pump - popped at about 28 psi - did it under water, saw some very very small leaks around gasket at same pressure. No pre pop air leaks from valve.
 
Skippydiesel

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Gentlemen - My son (a bit of 2/aficionado) may have found the problem - there appears to be a "Welsh" plug missing from the diaphragm side (probably blown off by me). It would be in the shape of a round cornered triangle. The plug covers three small holes that would have been letting unmetered fuel into the carb throat.
My son has already started making a replacement out of aluminium sheet. He is unlikely to be able to fashion an interference/press fit, as per original, so will use aviation gasket goo to secure it in place.
Fingers crossed, the flooding issue will have been fixed.
 

J D

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Gentlemen - My son (a bit of 2/aficionado) may have found the problem - there appears to be a "Welsh" plug missing from the diaphragm side (probably blown off by me). It would be in the shape of a round cornered triangle. The plug covers three small holes that would have been letting unmetered fuel into the carb throat.
My son has already started making a replacement out of aluminium sheet. He is unlikely to be able to fashion an interference/press fit, as per original, so will use aviation gasket goo to secure it in place.
Fingers crossed, the flooding issue will have been fixed.
Sounds promising.
There are very few sealants that will hold up inside a carburetor. I would fashion a new welch plug out of the base of an aluminum can so that it has a bit of a dome that you can flatten into place like a regular welch plug.
Good luck, keep us posted
 
Mad Professor

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Sounds promising.
There are very few sealants that will hold up inside a carburetor. I would fashion a new welch plug out of the base of an aluminum can so that it has a bit of a dome that you can flatten into place like a regular welch plug.
Good luck, keep us posted
The full carb kit might have the plug. Methacrylate/crazy glue hold up to fuels pretty good.
 
Mad Professor

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Is there a full carb (repair) kit available ?

If so where? - Stihl?
From $tihl/$teal will be expen$ive. From 034 IPL (pgs 38-39) their carb kit 1128 007 1065 , lists parts 3-10, does not list #14 the plug. That's curious?

1) Zama link below kit# RB-31 NIx trying to get kit or carbs from ZAMA!!! They only distribute through $teal dealers

Zamacorp

I think you need #4 from the metering side. 1 zama C3A.png

2) Tillotson makes rebuild kits for other man. carbs. Attached is the exChange catalog, a good resource to download. There are two kits for 034, one is for the Zama, I think the other is for the early 034 Tillotson

I think it's kit # Z-RK-031 , Zama code RB-31 (See above)

Both sources seem to include the plug in the rebuild kit (but not on $tihl IPL?). Good idea to spend a little extra on the full kit to have the parts in case you need them.

1 zama C3A kit.png

When you install the gaskets/diaphragms, put a thin coat of vasilene on them, then they won't get stuck if you have to go inside the carb again and reuse them
 

Attachments

  • Tillotson_Exchange_Catalog.pdf
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  • 1 zama C3A.png
    1 zama C3A.png
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  • 034 IPL.pdf
    2.1 MB · Views: 3
SteveSr

SteveSr

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Is there a full carb (repair) kit available ?

If so where? - Stihl?
Watch out. Zama used two different shapes of welch plugs in the C3 carb (assuming that is the one that you have). As far as making a welch plug fuggetaboutit! BOTH Walbro and Zama can't get the plugs to seal reliably using precision parts and factory tooling. They use a proprietary secondary sealant. Once you get the correct plug installed run a THIN bead water THIN of super glue around the edge of the plug. Put the carb on a shelf for 48 hours to make sure that the super glue cures completely. Be sure to clean the new plug and the recess in the carb with brake cleaner before installing.
 

J D

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Would probably be worth doing the rounds & talking to the local repair shops... If you're lucky you'll find one with a bin of leftover repair kits they'll let you look through. I'm not sure how unique of a size your one will be but a lot of people won't use them even if they're in a kit so it's worth a shot
 
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